Extendable divergent tail pipe propulsion unit

ABSTRACT

The deployable diverging part comprises a first portion ( 20 ) having an upstream end connected to the end wall ( 14 ) of the thruster, a ring-shaped second portion ( 22 ) that is movable between a retracted position and a deployed position in which it connects to the downstream end of the first portion ( 20 ) to extend it, and a deployment mechanism comprising a plurality of hinged arms ( 30 ). Means ( 50, 52 ) are provided in distributed manner at the periphery of the downstream end of the first portion and at the periphery of the upstream end of the ring to enable the ring ( 22 ) to be locked onto the downstream end of the first portion ( 20 ) when the ring is in its deployed position, and the deployment mechanism comprises at least four arms ( 30 ) co-operating with the ring ( 22 ) to form a hyperstatic assembly so that the ring can be displaced without significant deformation so as to be brought into the desired position to lock automatically and completely on the first portion ( 20 ) when it is deployed.

The present invention relates to a deployable diverging part of athruster.

The thrust from a thruster depends on the rate at which gas is ejectedand on the speed at which it is ejected. To optimize the speedparameter, it is necessary to have a diverging part with an outlet thatis of large diameter, particularly for a second or third stage of amultistage thruster. This leads to diverging parts that are long, whichis often difficult to make compatible with the space available. Onesolution consists in designing a diverging part that is deployable,which is of shorter length in its initial configuration and which can belengthened by putting one or more rings of the diverging part intoplace.

Deployable diverging parts are also used to match the outlet section ofthruster nozzles to ambient pressure, which pressure decreases from lowaltitudes close to the ground to high altitudes, such that as close aspossible an approximation to optimum thrust is always obtained in spiteof changing altitude.

In all these cases, it must be possible to deploy the deployable portionof the diverging part in a manner that is automatic and reliable, whileexpending a minimum amount of energy.

Various types of deployment mechanism have been proposed for deployablediverging parts, in particular mechanisms making use of cables, ofroller screws, of ball screws, of beams that can be rolled out, or of amembrane. Overall, those mechanisms are relatively bulky and give riseto a very large mass penalty, particularly for diverging parts of largediameter.

A deployment mechanism that does not present those drawbacks has alreadybeen proposed in the Applicant's U.S. Pat. No. 5,282,576. The divergingpart comprises a first portion whose upstream end is connected to theend wall of the thruster and a second portion in the form of a ring thatis movable between a retracted position in which it surrounds the firstportion of the diverging part, and a deployed position in which it isconnected to the downstream end of the first portion to extend it. Thedeployment mechanism comprises hinged arms each having one end connectedto the ring of the diverging part, and means for actuating the armsenabling the ring of the diverging part to be displaced from itsretracted position to its deployed position.

It is necessary to lock the ring of the diverging part in its deployedposition in order to prevent it from returning towards its retractedposition under thrust from the jet passing through it. In U.S. Pat. No.5,282,576, that locking is achieved by an over-center or “toggle” actionof the arms so as to avoid leaving the actuator means continuouslyactive after deployment, with the operation of the deployment mechanismbeing reversible.

An object of the present invention is to provide a deployable divergingpart of the same type as U.S. Pat. No. 5,282,576, but in which the ringis locked in the deployed position in a manner that is reliable, withoutrequiring any special geometrical configuration for the arms, and withthe deployment mechanism not being designed to be reversible.

This object is achieved by the facts that:

means are provided in distributed manner at the periphery of thedownstream end of the first portion and at the periphery of the upstreamend of the ring so as to enable the ring to be locked onto thedownstream end of the first portion when the ring is in its deployedposition; and

the deployment mechanism comprises at least four arms co-operating withthe ring to form a hyperstatic assembly so that the ring can be movedwithout significant deformation so as to be brought to the desiredposition for locking automatically and completely to the first portionwhen it is deployed.

The deployable diverging part of the invention is thus remarkable in itscombination of automatic locking of the ring of the diverging part onthe first portion thereof by locking means that are distributed aroundtheir periphery, and by the hyperstatic nature of the moving assemblywhich makes it possible to guide the ring of the diverging partaccurately to the exact deployed position required for locking to takeplace automatically.

Advantageously, the locking means comprise a plurality of flexibletongues co-operating with one or more corresponding recesses so as tosnap into the recess(es) when the ring reaches its deployed position.

Also advantageously, releasable locking means are provided to lock thering in its retracted position.

The invention will be better understood on reading the followingdescription given by way of non-limiting indication and with referenceto the accompanying drawings, in which:

FIG. 1 is a diagrammatic half-view in section showing a first embodimentof a deployable diverging part of the invention, with the ring of thediverging part in the retracted position;

FIG. 2 is a half-view in section similar to FIG. 1, but with the ring ofthe diverging part in the deployed position;

FIG. 3 is a plan view of an arm of the deployment mechanism of FIGS. 1and 2;

FIG. 4 is a detail view showing the locking means in the deployablediverging part of FIGS. 1 and 2 for locking the ring of the divergingpart on the first portion thereof, said locking means being shownimmediately before locking;

FIG. 5 is a detail view similar to FIG. 4, but after locking;

FIG. 6 is a diagrammatic half-view in section showing a secondembodiment of a deployable diverging part of the invention, with thering of the diverging part in the retracted position; and

FIG. 7 a half-view in section similar to FIG. 1, but with the ring ofthe diverging part in the deployed position.

In FIGS. 1 and 2, reference 10 designates a thruster body, e.g. a solidpropellant thruster whose combustion chamber 12 opens out through theend wall 14 of the thruster via a nozzle throat 16 which is extended bya first portion 20 of a deployable diverging part.

The upstream end of the portion 20 of the diverging part (“upstream” inthe gas flow direction) and the nozzle throat 16 are connected to theend wall 14 of the thruster by means of a cone when the nozzle is fixed,or by means of a flexible abutment 18 when the nozzle is articulated asin the case shown. By way of example, the abutment may be spherical andconstituted, in conventional manner, by alternating layers of metal orcomposite material and of elastomer bonded thereto.

The body and the end wall of the thruster, and also the nozzle throatand the portion 20 of the diverging part are normally internally coatedwith thermal protection material that ablates.

The deployable diverging part also comprises a ring 22 which, in theretracted position (FIG. 1) surrounds the portion 20, being coaxialthereabout, and in the deployed position (FIG. 2) connects to thedownstream end of the portion 20 and extends it so as to form adiverging part having an enlarged outlet diameter.

The ring 22 is held in the retracted position and is guided towards thedeployed position by means of four hinged arms 30 that are uniformlydistributed around the first portion 20 of the diverging part.

Each arm (FIGS. 1, 2, 3) comprises a first segment 32 hinged at a firstend to a lug 36 fixed to the outside wall of the first portion 20 of thediverging part (about an axis 33) and at a second end to a first end ofa second segment 34 (about an axis 35). At its second end, the segment34 is hinged to a lug 38 fixed to the outside wall of the ring (about anaxis 37). Each arm segment 32, 34 is made up of two parallel flanksrespectively referenced 32 a, 32 b, and 34 a, 34 b. The plane ofsymmetry P (FIG. 3) of each arm contains the axis A of the divergingpart, with the hinge axes 33, 35 and 37 at the ends of the segments 32and 34 being perpendicular to the plane P and to the axis A. As shown inFIG. 1, a device for locking the arm in its retracted position comprisesan abutment 40 secured to the segment 32 and provided with a stud 42which penetrates into a recess 39 in the lug 38. The stud 42 can bedisengaged from the recess 39 to release the arm 30 by pneumatic means,e.g. by connecting the stud to the piston of a pneumatic actuator, or bypyrotechnic means. There is no need to provide a locking device on eacharm 30, locking only one arm can suffice to hold the assembly in theretracted position.

When the arm 30 is released, it can deploy, with its segments 32 and 34rotating about their end hinge axes. While the arm is deploying, theposition of the plane of symmetry P remains unchanged.

In the example of FIGS. 1 to 3, the arm 30 is deployed by means of atorsion spring 44 mounted on the hinge axis 33. The spring 44 drives afluted outlet shaft 45 engaged with the segment 32.

To deploy the ring 22 of the diverging part, all four arms 30 arereleased simultaneously by unlocking the studs 42. When released in thisway, the springs 44 cause the arm segments 32 to pivot simultaneously,thereby deploying the arms simultaneously.

It will be observed that the assembly constituted by the four arms 30and the ring 22 is hyperstatic, which means that the ring 22 moveswithout deforming and remains constantly centered on the axis A. Thehyperstatic nature of the assembly thus makes it possible to provideaccurate guidance of the ring 22 towards its deployed position, and thearms are prevented from moving in non-synchronous manner. It will beobserved that this result can still be obtained-if a torsion spring ismounted on only some of the arms, or indeed on only one arm. In thiscase, the hyperstatic nature comes from the fact that four arms 30 areprovided. The number of arms could be greater than four, but that wouldincrease the mass of the mechanism without providing any real additionaladvantage.

According to a feature of the deployable diverging part of theinvention, means are provided at the periphery of the downstream end ofthe portion 20 and at the periphery of the upstream end of the ring 22to provide mutual locking when the ring reaches its deployed position.

In the example shown (FIGS. 1, 2, 4, and 5), these locking means areconstituted by a plurality of flexible tongues 50 fixed to the peripheryof the downstream end of the portion 20, on the outside thereof, and byan annular setback 52 formed at the upstream end of the ring 22, on theinside thereof.

When the ring 22 comes close to its fully deployed position, the insidewall 22 a of the ring 22 presses against the tongues 50, causing them tobe deflected towards the axis of the diverging part (FIG. 4). To thisend, each tongue 50 leaves a gap 51 between its free end and the outsidewall of the portion 20.

The position of the tongues 50 and the position of the setback 52 aredetermined so that the tongues snap into the setback 52 when the ring 22reaches the deployed position (FIG. 5). This ensures that the ring 22 islocked onto the portion 20. It will be observed that the accuracyprovided by the hyperstatic assembly makes this kind of automaticlocking possible. It will also be observed that the setback 52 could bereplaced by a plurality of recesses corresponding to the tongues.

In the embodiment of FIGS. 1 to 3, the arms are deployed by one or moretorsion springs. This solution is suitable when the diverging part isdeployed before the thruster is ignited, however the force developed bythe spring(s) would normally be insufficient to overcome the pressure ofthe gas jet if deployment were to be performed after ignition.

An embodiment that is suitable for deployment after the thruster hasbeen ignited is shown in FIGS. 6 and 7.

In this second embodiment, the portions of the diverging part whichcorrespond to portions of the embodiment shown in FIGS. 1 to 5 are giventhe same references and are not described again.

As can be seen in FIGS. 6 and 7, the arm 30 is held in the retractedstate and it is deployed by means of at least one actuator 60 whosecylinder 62 is hinged to a lug 64 fixed to the outside wall of theportion 20 and whose rod 66 is hinged at its end to the segment 32 ofthe arm 30. There is no need to provide a device for locking the arm 30in the retracted position.

The actuator 60 may be of pneumatic or hydraulic type. It is possible toprovide a single actuator, with simultaneous displacement of the otherarms being ensured by the hyperstatic assembly, or else to provide aplurality of arms with respective actuators. The ring 22 is locked onthe portion 20 in the same manner as that described with reference toFIGS. 4 and 5.

Other means may be provided for driving the deployment means whendeployment is to be performed after ignition. For example, it will bepossible to replace the torsion springs of the embodiment of FIGS. 1 to3 by one or more motors. In addition, it is naturally possible toprovide actuator or motor-driven drive even when deployment is performedbefore ignition. It is also possible to envisage driving deployment bypyrotechnic means.

Finally, it should be observed that the locking by means of tongues anda setback as shown in FIGS. 4 and 5 could easily be replaced by anyother known means enabling locking or snap-fastening to be achievedautomatically.

What is claimed is:
 1. A deployable deverging part for a thruster, thediverging part comprising: a first portion having an upstream endconnected to the end wall of the thruster; a second portion in the formof a ring that is moveable between a retracted position in which itsurrounds the first portion and a deployed position in which it isconnected to the downstream end of the first portion so as to extend it;and a deployment mechanism comprising at least four hinged arms eachhaving one end connected to the ring, and at least one arm having anarm-driving means enabling the ring to be moved from its retractedposition to its deployed position; means are provided in distributedmanner at the periphery of the downstream end of the first position andat the periphery of the upstream end of the ring so as to enable thering to be locked onto the downstream end of the first portion when thering is in its deployed position; and the at least four hinged armsco-operating with the ring to form a hyperstatic assembly, wherein theat least four hinged arms move in a substantially synchronous manner sothat the ring can be moved without significant deformation so as to bebrought to the desired position for locking automatically and completelyto the first portion when it is deployed.
 2. A diverging part accordingto claim 1, characterized in that the locking means comprise a pluralityof flexible tongues disposed on said first portion co-operating with oneor more corresponding recesses disposed on said second portion so as tosnap into the recesses when the ring reaches its deployed position.
 3. Adiverging part according to claim 1, characterized in that releasablelocking means are provided to lock the ring in its retracted position.4. A diverging part according to claim 3, in which each of the at leastfour hinged arms comprises a plurality of hinged segments characterizedin that the locking means are organized to prevent a segment of at leastone of the arms from moving relative to another segment of the same arm.5. A diverging part according to claim 1, characterized in that the atleast four hinged arms are moved into the deployed position by drivemeans mounted on a hinge of at least one of the at least four hingedarms.
 6. A diverging part according to claim 5, characterized in thatthe drive means are constituted by a torsion spring.
 7. A diverging partaccording to claim 1, characterized in the at least four hinged arms aremoved into the deployed position by drive means acting on a segment ofat least one of the at least four hinged arms.
 8. A diverging partaccording to claim 7, characterized in that the at least four hingedarms are moved into the deployed position by means of at least oneactuator mounted between the first portion and a segment of one of theat least four hinged arms.
 9. A diverging part according to claim 2,characterized in that releasable locking means are provided to lock thering in its retracted position.
 10. A diverging part according to claim4, characterized in that the at least four hinged arms are moved intothe deployed position by drive means mounted on a hinge of at least oneof the at least four hinged arms; and the drive means are constituted bya torsion spring.
 11. A diverging part according to claim 4,characterized in that the at least four hinged arms are moved into thedeployed position by drive means acting on a segment of at least one ofthe arms by means of at least one actuator mounted between the firstportion and a segment of one of the at least four hinged arms.